First Post: Time for a new battery?

Hi, My first post on here, a bit of background first; I purchased my 2003 C2 manual cabriolet about 6 weeks ago. Well looked after by the previous owner so not much required, though so far I have replaced the CD changer with the Mr12volt Bluetooth unit, replaced the CD holder with the storage shelf unit, and refreshed the caliper Porsche logo decals. Very happy so far. My question is about the battery. The previous owner kept it on a battery maintainer, but I have to keep it outside on the drive.l and don't have it connected to a charger/ maintainer. When the car is running the dash voltmeter shows around 13.5v and shortly after turning off the engine it will read about 12.5v. After a week the battery is often down to about 11.5v. I've not had any issues starting yet, but cranking is definitely a bit slower. Having checked the battery today it appears it's almost exactly 8 years old. My question is really whether this sounds normal or whether it sounds like it's due for replacement? I'm trying to avoid a situation where I drive somewhere then find I can't get back, I know batteries can fail quite suddenly! ​​​​​

Generally speaking an 8 year old battery is at end of life . But drive to your local parts store and have them do a load test . Really the only way to know what's going on inside . But in my opinion you are on borrowed time .

AAA aka Auto Club also sells batteries. Couple weeks ago my 996 would not start after refilling my tank. Called the Auto Club for a jump. They showed up, tested the battery and suggested they sell me a new battery. He was driving a pickup with a cover on the bed. Under the cover were approximately 20-30 batteries including my exact battery. $172 later I was on my way and he kept my five year old battery.

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Exactly as stated above. 8yrs is a long time for a car battery. I would replace with a new H7 agm battery. I just acquired a duralast platinum with 36 month warranty. I usually get 3-5 yrs max on batteries down south as the heat is a killer too. I wouldn�t chance getting stranded or have to deal with opening the frunk via cables�.

Thanks all, I think a replacement is the way I was leaning, the voltage jumps to 14v when running so assumed that it doesn't appear to be an alternator/ regulator issue. The car does have an old tracker fitted which I wonder might be causing unnecessary drain. The positive lead for it is connected straight to the battery, so I did consider just disconnecting it. My only concern is whether it's connected to the immobiliser, or purely just tracking. It's called a Cobra Trak Q, but can't find much about it on the internet, I believe it is now part of Vodafone (I'm in the UK BTW).

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Do this and do it now.

Will get and install a new battery this week thanks. Any thoughts on whether it would be ok to disconnect the tracker without causing an issue?

I can't imagine anything will happen if you disconnect the tracker .

There is an inline fuse for the tracker near the battery, assume I should just be able to pull that to quickly get my answer.

These cars drain the bateries in 3-4 weeks. It has to do with the factory alarm and electronics. The dash showing 13.5v while running is also normal. Change the battery as its due and drive the car more often

Why not put it on a tender?

The car is being driven once or twice per week. My question is really about understanding what is normal behaviour, so with its current use, I don't believe I should need a tender, though I will probably get one at some point anyway. It's clear from the other answers that the battery is due a replacement anyway as I don't want to end up stranded! Also the question about the tracker is also just to reduce current drain for something that is no longer used. I took the fuse put earlier and it fired up no problem.

This is the battery I have in my car, it's 8 yrs old and still going strong. I do drive it at least 4 days a week to work. Amazon Amazon

I replaced the battery with an Exide 72Ah lead acid type, not the biggest capacity but it get sold reviews and come with 4 year warranty for �62 (US$80) and I've also bought a battery maintainer so it should do me fine. Cranking is definitely livelier and it now reads 12.6v on the multimeter after driving.

Was that 12.6v with the engine off? If so then all good. If the engine was running it means your alternator or voltage regulator is bad.

Yes, by after driving, I mean engine off, and holding a higher voltage in the following days.